Most lacrimal sac tumors are primary tumors and only a few are metastatic [4]. Approximately 75% of primary tumors are epithelial tumors, while the remaining 25% include malignant lymphoma, sarcoma, and malignant melanoma; in either case, a high percentage of tumors are malignant [1, 10, 11]. Most primary epithelial tumors are squamous cell carcinoma, with other types reported including basal cell carcinoma, adenocarcinoma, transitional cell carcinoma, and adenoid cystic carcinoma [1, 3]. Papillary carcinoma and mucoepidermoid carcinoma have a relatively good prognosis, while squamous cell carcinoma, adenocarcinoma, and transitional cell carcinoma reportedly have a poor prognosis [9, 12]. Adenocarcinoma reportedly accounts for only 3% to 4% of primary lacrimal sac epithelial tumors [3,4,5]; a possible origin of adenocarcinoma of the lacrimal sac is thought to be the seromucinous gland in the lacrimal sac [10, 11, 13].

There is no TNM classification for staging lacrimal sac carcinoma; instead, the classification by Jones et al. is used [14]. Stage 1 is defined as lacrimation, stage 2 as dacryocystitis, stage 3 as painless swelling that does not deform with pressure, and stage 4 as invasion of surrounding tissues. This patient was diagnosed at stage 4. According to the literature, early diagnosis is typically difficult [1, 2]. This is partly because the condition is difficult to differentiate from dacryocystitis based on physical findings in stages 1 and 2. However, MRI effectively differentiates between the 2 entities. As we saw in our patient, lacrimal sac carcinoma is characterized by low signal intensity on T1- and T2-weighted images and high signal intensity with gadolinium contrast. Dacryocystitis appears with high signal intensity on T2-weighted images, making it possible to differentiate between the lesions [15, 16]. If there is any possibility of neoplastic disease, it is advisable to perform MRI proactively.

There is no established method for treating lacrimal sac cancer, but many reports describe aiming for complete surgical resection with the frequent addition of postoperative radiation therapy or chemotherapy. The effectiveness of chemotherapy is unclear from reports to date [1, 3, 4]. The 5-year overall survival rate is about 80% for this type of cancer, with local recurrence reportedly the most frequent type of recurrence [3, 4]. Because of the anatomic structure around the tumor, extensive resection is often required to achieve complete removal. The mortality rate is reportedly significantly lower in patients undergoing extended resection, including lateral nasal resection, than in those undergoing local resection [9], but it is difficult to avoid a significant impact on cosmetic appearance. Radiation therapy is an effective treatment for preserving morphology. Song et al. reported that, in patients with lacrimal sac squamous cell carcinoma who refuse or are unable to undergo surgery, radiation therapy alone or chemoradiotherapy demonstrates overall survival comparable to that of patients who underwent surgery as initial treatment [3, 8].

Because adenocarcinoma of the lacrimal sac is extremely rare, data on outcomes after treatment are limited to case reports. The reports of lacrimal sac adenocarcinoma with described treatment courses are summarized in chronological order in Table 1 [5, 12, 17,18,19,20,21,22,23,24,25]. In addition to surgery, radiation therapy, and chemotherapy, there are 2 case reports describing the use of hormone therapy for patients with androgen receptor–positive cancer; 1 of these patients achieved long-term progression-free survival with hormone therapy alone [21, 23]. Radiation therapy was administered in 13 of 15 patients. In addition to our patient, Wright et al. reported 4 patients treated with radiation alone, but all 4 experienced recurrence within 2 years [12]. However, all 4 of these patients were treated in the 1970s and 1980s, before the widespread use of 3-dimensional radiation therapy planning devices. Although the total dose and number of fractions was not specified for every patient, most of the described radiation therapy courses used a total dose of 50 Gy or more; the total dose in those cases was lower than in more recent reports [2, 3, 5, 22, 24, 25]. Although the optimal dose is unclear due to the small number of cases of definitive radiation therapy, a higher total dose may improve tumor control. Our patient received a total dose of 70 Gy and achieved 5-year recurrence-free survival. In a report by Okazaki et al., 3-year recurrence-free survival was observed after irradiation with 70 Gy for a locally recurrent tumor 2 years after surgery [25]. The further accumulation of case reports is required to establish the optimal radiation dose.

Radiation retinopathy is among the causes of secondary neovascular glaucoma, which can lead to blindness. It is believed that radiation damages retinal vascular endothelial cells, causing impaired retinal blood flow and hypoxia, which in turn releases vascular endothelial growth factor (VEGF) and induces neovascularization of the iris and the angle [26]. In general, increasing the total dose of radiation therapy increases the therapeutic effect but also increases the adverse effects on normal tissue. The incidence of radiation retinopathy reportedly increases with increasing radiation dose, rising rapidly when the radiation dose exceeds 50 Gy [26, 27]. Similar to our report, previous reports of radiation therapy for lacrimal sac carcinoma have also noted complications such as decreased vision in the affected eye, eye pain, and neovascular glaucoma [3, 28]. However, in recent reports of radiation therapy for malignant lacrimal sac tumors managed without surgery, a total dose of 60 to 70 Gy has been administered [2, 3, 8, 28]. Reducing the total dose to prevent side effects may increase the risk of recurrence. High-precision radiotherapy, such as intensity-modulated radiation therapy (IMRT), particle therapy, and brachytherapy, is regarded as a method that reduces adverse effects while administering high doses. Previous studies reported the use of highly concentrated brachytherapy and proton-beam therapy as a means of reducing the side effects of radiation; however, only a limited number of facilities provide these treatments [22, 24]. Although few studies have examined the efficacy of IMRT for lacrimal sac carcinoma, in radiation therapy for head and neck cancer, fewer late adverse effects were associated with IMRT than with three-dimensional radiation therapy; therefore, it may also be useful for reducing the adverse effects of radiation therapy for lacrimal sac carcinoma [8, 29].